REL-30 IO backports from 4.x

 - Allow di_retire_device() to succeed when device is in use by ZFS (OS-55)
 - Add new FMA diagnosis engines (OS-93)
 - Slow IO error detection (OS-62)
 - SD failfast improvements (OS-58)
 - mptsas target removal code removed (OS-59)
 - ZFS retire agent improvements (OS-65)
 - mptsas watchdog resolution considered way to low for accurate CMD timeouts (OS-60)